1. Field of the Invention
This invention relates generally to the contacting of FCC feeds with catalyst for ultra-short time periods. More specifically this invention relates to a method and apparatus for disengaging hydrocarbons and from catalyst particles.
2. Description of the Prior Art
There are a number of continuous cyclical processes employing fluidized solid techniques in which an at least partially liquid phase stream containing hydrocarbon compounds contacts the fluidized solids in a contacting zone and carbonaceous or other fouling materials are deposited on tile solids. The solids are conveyed during the course of the cycle to another zone where foulants are removed in a rejuvenation section or, more specifically, in most cases carbon deposits are at least partially removed by combustion in an oxygen-containing medium. The solids from the rejuvenation section are subsequently withdrawn and reintroduced in whole or in part to the contacting zone. The solids may be catalytic materials or inert solids.
One of the more important processes of this nature is the fluid catalytic cracking (FCC) process for the conversion of relatively high-boiling hydrocarbons to lighter hydrocarbons. The hydrocarbon feed is contacted in one or more reaction zones with the particulate cracking catalyst maintained in a fluidized state under conditions suitable for the conversion of hydrocarbons.
The processing of increasingly heavier feeds in FCC type processes and the tendency of such feeds to elevate coke production and yield undesirable products has led to new methods of contacting feeds with catalyst. Recently, methods of contacting FCC catalyst for very short contact periods have been of particular interest. Falling-curtain type arrangements for contacting feed are known from U.S. Pat. No. 2,935,466; the contents of which are hereby incorporated by reference. In U.S. Pat. No. 4,985,136, an FCC feed contacts a falling-curtain of catalyst for a contact time of less than 1 second followed by a quick separation. U.S. Pat. No. 5,296,131, the contents of which are hereby incorporated by reference, discloses a similar ultra short contact time process that uses an alternate arrangement for the falling catalyst curtain. The ultra short contact time system improves selectivity to gasoline while decreasing coke and dry gas production by using high activity catalyst that previously contacted the feed for a relatively short period of time. The inventions are specifically directed to zeolite catalysts having high activity. Additional arrangements for performing such feed contacting are known from U.S. Pat. Nos. 4,435,272, 4,944,845, and 5,462,652.
The type of injection desired for short contact time arrangements has received particular attention in the above referenced patents. The feed may be formed into a jet by an array of identical feed injection streams or by an extended orifice that uniformly contacts a stream of catalyst flowing in a compatible pattern. The feed injection is arranged to shoot the feed into a relatively thin band of catalyst that falls in a direction perpendicular to the flow of jets.
Aside from uniform feed and catalyst contacting, short contact time also requires good separation between the catalyst and hydrocarbons. The above described prior art typically directs the catalyst and vapor mixture into a conduit that communicates with a downstream separation device. Therefore, contact of the hydrocarbons with the catalyst will continue for a substantial period of time as it flows to the separation device and while it is in the separation device.